/cc @Hixie

@HansMuller are you expecting this to return null?

Ideally we'd have a test for this too...

The existing Scaffold.of(context)?.appBarAnimation should not have included the '?.'.

The Scaffold.of() call is within a Builder widget that only exists so that the Scaffold.of() call will succeed.

So it should not be returning null? It apparently is...

The problem appears to be the Scaffold's key:
https://github.com/flutter/flutter/blob/master/examples/flutter_gallery/lib/gallery/home.dart#L102

I don't think there's any need for _homeKey and removing it fixes the problem.

I'm still seeing Scaffold.of() returning null after removing the _homeKey

Yes, sorry about the misdirection. Although the problem seemed to have gone away after removing _homeKey (which I still don't think is needed), trying the remedy again fails for me too.

Scaffold.of() seems to be returning null due to some sort of race involving the hero animation subsystem.

If the Builder within Gallery's AppBar is invoked while the animation is still in progress, then the AppBar widgets will be descendants of the HeroQuestState transition widgets and will not have a Scaffold ancestor.

@Hixie

Oh, that makes sense. During the page transition, the AppBar is a hero that persists during the transition. When it is transitioning, it isn't a child of the scaffold.

Changed this to use a GlobalKey to locate the scaffold

PTAL

LGTM!

Ideally this would have a test -- in fact I'm surprised the smoketest didn't catch this.